Transferring control to another service provider in e-commerce application

I am creating a ecommerce application. I will transferring the control on to online payment website.

AS per their sample code they are creating a form with parameters like NAme, Phone No., AMount,Success URL and Failure URL and posting it by adding a Literal control to form and using <form Method='post'>
Like:
string strForm ="<form id="PostForm" name="PostForm" action="https://OnlinePaymentCompany.com/_payment" method="POST"> <input type="hidden" name="lastname" value="Gupta"> <input type="hidden" name="address2" value=""> <input type="hidden" name="udf5" value=""> <input type="hidden" name="service_provider" value=""> <input type="hidden" name="curl" value=""> <input type="hid ...